Children with growth hormone deficiency are currently treated with recombinant human growth hormone (hGH) by daily injection. This 6 month phase I/II research study will investigate the safety and efficacy of a new sustained release formulation of recombinant human growth hormone, ProLease hGH which will be given by monthly injection. Two groups of growth hormone deficient subjects will be studied: Children who have been treated with recombinant human growth hormone for at least one year prior to study, and naive subjects who have not yet received growth hormone. Subjects will be admitted to the CRC. Blood testing for measurement of growth hormone and growth hormone dependent growth factors will be done prior to ProLease hGH injection then at 6, 12, 18, 24, 36, and 48 hours. Subjects will then be discharged from the CRC to have twice weekly blood testing for the remainder of that month. Subjects with prior growth hormone treatment will undergo a second cycle of intensive sampling with the second injection, whereas naive subjects will just have a single cycle of intensive testing. Additional injections will be followed by measurement of growth hormone 24 hours post-injection and then weekly. The study will continue for 6 months. Only the intensive sampling portion of this study will be done on the CRC, the outpatient studies will be performed at Children's Memorial Hospital. Growth rate will be assessed at 3 and 6 month and changes in bone age at baseline and 6 months. Subjects will be examined, reviewed for adverse effects and have blood testing for safety at monthly intervals throughout the study.